The effect of grazing Lotus corniculatus during late summer-autumn on reproductive efficiency and wool production in ewes

A grazing experiment was conducted at Massey University (Palmerston North, New Zealand) over 80 days in the late summer-autumn of 1998 (9 February-29 April). Reproductive performance and wool growth of ewes grazing on Lotus c orniculatus (birdsfoot trefoil) were compared with those of ewes grazing pe rennial ryegrass-white clover pasture. A rotational grazing system with 210 mixed-age dry ewes (59.8+/-0.9 kg/ewe) was used, with 80 ewes grazing past ure [1 g of condensed tannin (CT) per kg dry matter (DM)] and 130 ewes graz ing L. corniculatus (24 g CT/kg DM). Half of the ewes grazing L. corniculat us were supplemented orally, twice daily, with polyethylene glycol (PEG; MW , 3500) to inactivate the CTs. The effect of forage species and PEG supplementation on voluntary feed inta ke (VFI), reproductive performance (as measured by ovulation rate), and woo l production was measured during 4 synchronised oestrous cycles. The ewes w ere restricted to maintenance feeding during the first 10 days of each oest rous cycle and then increased to ad libitum for the 6 days leading up to an d including ovulation. In vitro organic matter digestibility in the selecte d diet was higher for lotus than for pasture (0.80 v. 0.76), with L. cornic ulatus containing less nitrogen than pasture (36.5 v. 40.8 g/kg organic mat ter). Ewes grazing on L. corniculatus produced 11% more wool and had an ovulation rate up to 14% higher than ewes grazing pasture, with neither parameter be ing affected by PEG supplementation. Higher mean ovulation rates of ewes gr azing L. corniculatus were due to increases in fecundity (multiple ovulatio ns/ovulating ewe; P < 0.05), with no effect on ewes cycling/ewes mated. Thr ee cycles of grazing on L. corniculatus were required to achieve the maximu m response in multiple ovulation, but most of this was achieved after 2 cyc les. As the VFI of ewes grazing on L. corniculatus was not greater than tha t of ewes grazing pasture, the greater wool production and higher ovulation rate of ewes grazing this forage was due to improved efficiency of feed ut ilisation. It was concluded that feeding ewes L. corniculatus increased the efficiency of both reproduction and wool production without increasing VFI .